1. Field of the Invention
The present invention relates to an optical recording medium, an optical recording method, and an optical recording device, and particularly to an optical recording medium capable of recording information therein, reproducing the information thereof, and overwriting therein by exposing them to light beams, thereby causing a change in optical properties in the transmittance and reflectivity of the recording material constituting the media.
2. Description of the Related Art
a. Related Art Concerning an Optical Recording Medium Having Overwritable Capability (for Information Recording):
(1) A recording medium using a cyanine dye as a recording material: disclosed in Japanese Patent Laid-Open Nos. 82093/1982, 56892/1983, 112790/1983, 114989/1983, 85791/1984, 83236/1985, 89842/1985, and 25886/1986.
(2) A recording medium using a phthalocyanine dye as a recording material: disclosed in Japanese Patent Laid-Open Nos. 150243/1986, 177287/1986, 154888/1986, 246091/1986, 39286/1987, 37991/1988, and 39888/1988.
b. Related Art Concerning Compact Disc Recordable (CD-R) Which is Overwritable:
(1) Those using the combination of a cyanine dye and a metal reflective layer as a recording material: disclosed in Japanese Patent Laid-Open Nos. 159842/1989, 42652/1990, 13656/1990, and 168446/1990.
(2) Those using a phthalocyanine dye (azaanulene dye) as a recording material: disclosed in Japanese Patent Laid-Open Nos. 176585/1989, 215466/1991, 113886/1992, 226390/1992, 1272/1993, 171052/1993, 116456/1993, 268227/1995, and 314897/1995.
(3) Those using an azo metal chelate dye as a recording material: disclosed in Japanese Patent Laid-Open Nos. 46186/1992, 141489/1992, 361088/1992, 279580/1993, 51673/1995, 161069/1995, 37272/1995, 71867/1995, 231866/1996, and 295811/1996.
c. Related Art Concerning a Digital Versatile Disc Recordable (DVD-R) Having a Large Capacity:
(1) Those using the combination of a cyanine dye and a metal reflective layer as a recording material: reported in PIONEER RandD vol. 6, No. 2 (1996), xe2x80x9cDevelopment of DVD-Recordablexe2x80x9d and xe2x80x9cFundamental Development of DVD-R dye discxe2x80x9d; ISOM/ODS ""96 (1996), and xe2x80x9cHigh Density of Recording on Dye Material Disc Approach for 4.7Gxe2x80x9d.
(2) Those using a polymethine dye as a recording material: disclosed in Japanese Patent Laid-Open Nos. 83577/1998, 119434/1998, 149583/1998, 188339/1998 and 278426/1998.
(3) Those using the combination of a polymethine dye and an optical stabilizing material as a recording material: disclosed in Japanese Patent Laid-Open No. 109475/1998, 109476/1998, 134413/1998 and 166739/1998.
(4) Those using the combination of an azo metal chelate dye and a metal reflective layer as a recording material; disclosed in Japanese Patent Publication No. 67438/1993 and Japanese Patent Laid-Open Nos. 161069/1995, 156408/1996, 231866/1996, 332772/1996, 58123/1997, 175031/1997, 193545/1998, 274732/1998, 277703/1997, 6644/1998, 6650/1998, 6651/1998, 36693/1998, 44606/1998, 58828/1998, 86519/1998, 149584/1998, 157293/1998, 157300/1998, 157301/1998, 157302/1998, 181199/1998, 181201/1998, 181203/1998, 181206/1998, 188340/1998, 188341/1998, 188358/1998, 208303/1998, 214423/1998, 228671/1998, and 12483/1999.
(5) Those using the combination of a tetraazaporphyrin (polphyrazine) dye and a metal reflective layer as a recording material: disclosed in Japanese Patent Laid-Open No. 267562/1997, 309268/1997 and 856/1998.
(6) Those using, as a recording material, the combination of a dye other than those described above and a metal reflective layer: disclosed in Japanese Patent Laid-Open Nos. 86517/1998, 93788/1998, 226172/1998, 244752/1998, 287819/1998, 297103/1998, 309871/1998, and 309872/1998.
(7) Those using, as a recording material, the combination of a cyanine dye, an azo metal chelate dye (salt forming dye) and a metal reflective layer: disclosed in Japanese Patent Publication No. 51682/1995 and Japanese Patent Laid-Open No. 34499/1999, WO98/29257, Japanese Patent Laid-Open Nos. 323478/1997, 195242/1999, 250505/1999, 168237/2000, 190641/2000, 190642/2000 and 198273/2000.
(8) Those using, as a recording material, the combination of a formazan (metal chelate) dye and a dye other than those described above: disclosed in Japanese Patent No. 2791944, Japanese Patent Laid-Open Nos. 295079/1996, 95520/1997, 193546/1997 and 337958/1998.
(9) Those using, as a recording material, the combination of a dipyrromethene (metal chelate) dye and a dye other than those described above: Japanese Patent Laid-Open Nos. 162430/1998, 166732/1998, 226172/1998, 42858/1999, 92682/1999, 165465/1998, 208111/1999, 227332/1999, 227333/1999, 255774/1999 and 256057/1999.
As described above, a number of optical recording media have been so far proposed. Now, DVD-R is under development as a next generation disc with a large capacity. To increase the recording capacity of DVD-R, development of various recording materials that can minimize the size of a recording pit, adoption of image compression techniques such as MPEG 2 and technical development to shorten the wavelength of a semiconductor laser for the recording pit reading are necessary.
An AlGaInP laser diode having a wavelength of 670 nm is the only red semiconductor laser available in the market for use in a bar code reader and a measuring instrument. With a trend toward high-density optical discs, the red semiconductor laser has been introduced into the optical storage market.
To standardize a driving system for a DVD, laser diodes having wavelengths of 630 and 670 nm are employed now for a light source. On the other hand, driving systems for a read-only DVD-ROM are put on the market, with the light sources for the driving systems having a wavelength of about 650 nm. Under such circumstances, the most preferred are DVD-R media capable of recording information therein and reading the information therefrom at wavelengths of 630 to 690 nm. A squarylium compound can be given as one example of the materials used for a recording layer of an optical recording medium which carries out recording and reading by the light pickup using a laser having a wavelength of 630 to 690 nm. The squarylium compound however is not generally suited for use in an optical recording medium because of insufficient photo stability. An azo metal chelate compound, on the other hand, can be given as one example of a dye having high light resistance. However, it involves the problem that the reflectivity is insufficient when it is used alone as a recording material.
An object of the present invention is therefore to provide a recording material for an optical recording medium suited for a DVD-R system using a semiconductor laser having an oscillation wavelength in a short wavelength region compared with the above-described conventional system, an optical recording medium showing excellent light resistance and shelf life, in particular, when it contains a squarylium compound; an optical recording method and an optical recording device each using the above-described optical recording medium.
The present inventors have carried out an extensive investigation. As a result, it has been found that an optical recording medium with high reliability, high reflectivity and low jitter can be provided by using a metal-chelated squarylium compound, thereby improving optical stability; by mixing therewith an azo metal chelate compound having high light resistance, thereby imparting the recording medium with higher light resistance and higher shelf life; and by using a metal-chelated squarylium compound, thereby improving the absorption coefficient of the recording medium, leading to the completion of the first and second optical recording media of the present invention.
It has also been found that an optical recording medium suitable for use in a next-generation optical disc system with a large capacity using a semiconductor laser having an oscillation wavelength of 690 nm or less and at the same time having excellent light resistance and shelf life is available by using, as a main component of a recording layer, a mixture of a dye obtained by metal chelating a squarylium compound and a formazan metal chelate compound, leading to the completion of the third optical recording medium of the present invention.
It has further been found that an optical recording medium suitable for use in a next-generation optical disc system with a large capacity using a semiconductor laser having an oscillation wavelength of 690 nm or less is available by using as the main component of a recording layer, a mixture of a squarylium compound and a formazan metal chelate compound, leading to the completion of the fourth optical recording medium of the present invention.
The first recording medium of the present invention is described below in  less than A-1 greater than . Preferred embodiments of the first optical recording medium will be described below in  less than A-2 greater than  to  less than A-12 greater than .
 less than A-1 greater than 
An optical recording medium comprising a substrate and at least a recording layer disposed on the substrate, the recording layer comprises: at least one squarylium metal chelate compound which comprises a squarylium compound and a metal; and at least one azo metal chelate compound which comprises another metal and an azo compound expressed by the following formula (A-I): 
where A and B each independently expresses a residue forming one of a) a heterocyclic ring which may comprise a substituent and b) aromatic ring which may comprise a substituent, by combination with corresponding carbon atoms respectively bonded to A or B, and X expresses an active-hydrogen-containing substituent group.
 less than A-2 greater than 
The optical recording medium according to  less than A-1 greater than , wherein a contained amount of the squarylium metal chelate compound and the azo metal chelate compound are at a weight ratio ranging from 90:10 to 20:80.
 less than A-3 greater than 
The optical recording medium according to  less than A-1 greater than , wherein the metal atom of the azo metal chelate compound is at least one metal atom selected from the group consisting of manganese, cobalt, nickel and copper.
 less than A-4 greater than 
The optical recording medium according to  less than A-1 greater than , wherein the azo metal chelate compound is ionized and forms a salt with another compound ion.
 less than A-5 greater than 
The optical recording medium according to  less than A-4 greater than , wherein the another compound ion has an amino group.
 less than A-6 greater than 
The optical recording medium according to  less than A-1 greater than , wherein the squarylium metal chelate compound is expressed by the following formula (A-II): 
where, R1 and R2 are substituent groups which may be the same or may be different, and each expresses a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group which may have a substituent; M1 expresses a metal atom having a coordination capacity; Z expresses an aryl group which may have a substituent, a heterocyclic group which may have a substituent, or Yxe2x95x90CHxe2x80x94 (Y expresses a heterocyclic group which may have a substituent); and m1 stands for an integer of 2 or 3.
 less than A-7 greater than 
The optical recording medium of according to  less than A-6 greater than , wherein Z in the formula (A-II) is expressed by the following formula (A-IIxe2x80x94II): 
where, R3 and R4 may be the same or may be different and each expresses an alkyl group which may have a substituent, or R3 and R4 may form an alicyclic hydrocarbon ring or a heterocyclic ring by combination with adjacent carbon atoms; R5 expresses a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, or an aryl group which may have a substituent; R6 expresses a halogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent, a nitro group, a cyano group, or an alkoxy group which may have a substituent, n stands for an integer of 0 to 4, with the proviso that when n stands for 2 to 4, R6 may be the same or may be different to each other and by combination with the adjacent two carbon atoms form an aromatic ring which may have a substituent.
 less than A-8 greater than 
The optical recording medium according to  less than A-6 greater than , wherein M1 expresses aluminum.
 less than A-9 greater than 
The optical recording medium of according to  less than A-1 greater than , wherein a single layer of the recording layer has a refractive index (n) of 1.5xe2x89xa6nxe2x89xa63.0 a refractive index (n) of a single layer of the recording layer is 1.5xe2x89xa6nxe2x89xa63.0, and an extinction coefficient (k) is 0.02xe2x89xa6kxe2x89xa60.3 against a light having a wavelength in the range of recording or reproducing wavelength xc2x15 nm.
 less than A-10 greater than 
The optical recording medium according to  less than A-1 greater than , further comprising a reflective layer containing gold, silver, copper, aluminum or an alloy thereof
 less than A-11 greater than 
The optical recording medium according to  less than A-1 greater than , wherein a track pitch on the substrate falls within a range of 0.7 to 0.8 xcexcm, and a groove width at a half bandwidth falls within a range of 0.18 to 0.40 xcexcm.
 less than A-12 greater than 
The optical recording medium according to  less than A-1 greater than , wherein the optical recording medium can be recorded at a wavelength of 600 to 720 nm.
In the embodiments  less than A-1 greater than  to  less than A-8 greater than  and  less than A-12 greater than , optical information recording media capable of recording and reading by a laser light within a wavelength range of 600 nm to 720 nm, and having excellent light resistance and shelf life can be provided. In particular, the optical recording media obtained above are superior in light resistance to those using a squarylium metal chelate compound alone.
In the embodiments  less than A-9 greater than  to  less than A-11 greater than , optical recording media, in addition to having the above-described advantages, capable of recording and reading at a stably high reflectivity and high degree of modulation can be provided.
The second optical recording medium of the present invention is described below in  less than B-1 greater than . The preferred embodiments of the second optical recording medium will be described below in  less than B-2 greater than  to  less than B-10 greater than .
 less than B-1 greater than 
An optical recording medium having a substrate and at least a recording layer disposed on the substrate, the recording layer comprising: at least one squarylium metal chelate compound which comprises a squarylium compound and a metal; and at least one azo metal chelate compound which comprises another metal and an azo compound expressed by the following formula (B-I): 
where A expresses a residue forming a heterocyclic ring which may have a substituent by combination with both the carbon atom and the nitrogen atom bonded to A, and B expresses a residue forming one of a) an aromatic ring which may have a substituent and b) a heterocyclic ring which may have a substituent, by combination with the two carbon atoms bonded to B, and X expresses an active-hydrogen-containing substituent group.
 less than B-2 greater than 
The optical recording medium according to  less than B-1 greater than , wherein the squarylium metal chelate compound and the azo metal chelate compound are contained in the recording layer at a weight ratio of 90:10 to 20:80.
 less than B-3 greater than 
The optical recording medium according to  less than B-1 greater than , wherein the metal atom of the azo metal chelate compound is at least one metal atom selected from the group consisting of manganese, cobalt, nickel and copper.
 less than B-4 greater than 
The optical recording medium according to  less than B-1 greater than , wherein the squarylium metal chelate compound is expressed by the following formula (A-II): 
where, R1 and R2 are substituent groups which may be the same or may be different, and each expresses a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent or a heterocyclic group which may have a substituent; M1 expresses a metal atom having a coordination capacity; Z expresses an aryl group which may have a substituent, a heterocyclic group which may have a substituent, or Yxe2x95x90CHxe2x80x94 (Y expresses a heterocyclic group which may have a substituent); and m1 stands for an integer of 2 or 3.
 less than B-5 greater than 
The optical recording medium of  less than B-3 greater than , wherein Z in the formula (A-II) is expressed by the following formula (A-II-II): 
where, R3 and R4 may be the same or may be different and each expresses an alkyl group which may have a substituent, or R3 and R4 form an alicyclic hydrocarbon ring or a heterocyclic ring by combination with the adjacent carbon atoms; R5 expresses a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent or an aryl group which may have a substituent; R6 expresses a halogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent, a nitro group, a cyano group, or an alkoxy group which may have a substituent, n stands for an integer of 0 to 4, with the proviso that when n stands for 2 to 4, R6 may be the same or may be different to each other and form an aromatic ring which may have a substituent, by combination with the adjacent two carbon atoms.
 less than B-6 greater than 
The optical recording medium according to  less than B-3 greater than , wherein M1 expresses aluminum.
 less than B-7 greater than 
The optical recording medium according to  less than B-1 greater than , wherein a refractive index (n) of a single layer of the recording layer is 1.5xe2x89xa6nxe2x89xa63.0 and an extinction coefficient (k) is 0.02xe2x89xa6kxe2x89xa60.3 against the light having a wavelength range of a recording or reproducing wavelength xc2x15 nm.
 less than B-8 greater than 
The optical recording medium of  less than B-1 greater than , further comprising a reflective layer containing gold, silver, copper, aluminum or an alloy thereof.
 less than B-9 greater than 
The optical recording medium according to  less than B-1 greater than , wherein a track pitch on the substrate falls within a range of 0.7 to 0.8 xcexcm, and groove width at a half bandwidth falls within a range of 0.18 to 0.40 xcexcm.
 less than B-10 greater than 
The optical recording medium according to  less than B-1 greater than , wherein the optical recording medium is recordable at a wavelength of 600 to 720 nm.
In the embodiments of  less than B-1 greater than  to  less than B-6 greater than  and  less than B-10 greater than , optical information recording media capable of recording and reading by a laser light within a wavelength range of 600 nm to 720 nm, and having excellent light resistance and shelf life can be provided. In particular, the optical recording media obtained above are superior in light resistance to those using a squarylium metal chelate compound alone.
In the embodiments  less than B-7 greater than  to  less than B-9 greater than , optical recording media, in addition to having the above-described advantages, capable of recording and reading at a stably high reflectivity and high degree of modulation can be provided.
The third optical recording medium of the present invention is described below in  less than C-1 greater than . The preferred embodiments of the second optical recording medium will be described below in  less than C-2 greater than  to  less than C-10 greater than .
 less than C-1 greater than 
An optical recording medium comprising a substrate and at least a recording layer disposed on the substrate, the recording layer comprises: at least one squarylium metal chelate compound which comprises a squarylium compound and a metal; and at least one formazan metal chelate compound which comprises another metal and at least one of a formazan compound expressed by one of the following formulae (C-I) and (C-II): 
where, Z expresses a residue forming a 5-membered or 6-membered nitrogen-containing heterocyclic ring which may have a substituent by combination with both the carbon atom and the nitrogen atom bonded to Z, and may be condensed with another aromatic ring; A expresses an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkylcarbonyl group which may have a substituent, an arylcarbonyl group which may have a substituent, an alkenyl group which may have a substituent, a heterocyclic residue which may have a substituent, or an alkoxycarbonyl group which may have a substituent; and B expresses an alkyl group which may have a substituent, an alkenyl group which may have a substituent or an aryl group which may have a substituent, 
where, Z1 and Z2 each expresses a residue forming a 5-membered or 6-membered nitrogen-containing heterocyclic ring which may have a substituent by combination with both the carbon atom and the nitrogen atom bonded to Z1 and Z2, respectively, and may be condensed with another aromatic ring; A1 and A2 each independently expresses an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkylcarbonyl group which may have a substituent, an arylcarbonyl group which may have a substituent, an alkenyl group which may have a substituent, a heterocyclic residue which may have a substituent, or an alkoxycarbonyl group which may have a substituent; B1 and B2 each independently expresses an alkylene group which may have a substituent or an arylene group which may have a substituent; W expresses xe2x80x94CH2xe2x80x94 or xe2x80x94SO2xe2x80x94; and n stands for an integer of 0 or 1.
 less than C-2 greater than 
The optical recording medium according to  less than C-1 greater than , wherein the squarylium metal chelate compound and the formazan metal chelate compound are contained in the recording layer at a weight ratio of 90:10 to 50:50.
 less than C-3 greater than 
The optical recording medium according to  less than C-1 greater than , wherein the metal atom of the formazan metal chelate compound is at least one metal atom selected from the group consisting of vanadium, manganese, iron, cobalt, nickel, copper, zinc and palladium, and oxides or halides thereof.
 less than C-4 greater than 
The optical recording medium according to  less than C-1 greater than , wherein the squarylium metal chelate compound is expressed by the following formula (A-II): 
where, R1 and R2 are substituent groups which may be the same or may be different, and each expresses a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent or a heterocyclic group which may have a substituent; M1 expresses a metal atom having a coordination capacity; Z expresses an aryl group which may have a substituent, a heterocyclic group which may have a substituent, or Yxe2x95x90CHxe2x80x94 (Y representing a heterocyclic group which may have a substituent); and m1 stands for an integer of 2 or 3.
 less than C-5 greater than 
The optical recording medium according to  less than C-4 greater than , wherein Z in the formula (A-II) is expressed by the following formula (A-II-II): 
where, R3 and R4 may be the same or may be different and each expresses an alkyl group which may have a substituent, or R3 and R4 form an alicyclic hydrocarbon ring or a heterocyclic ring by combination with the adjacent carbon atoms; R5 expresses a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, or an aryl group which may have a substituent; R6 expresses a halogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent, a nitro group, a cyano group, or an alkoxy group which may have a substituent, n stands for a n integer of 0 to 4, with the proviso that when n stands for 2 to 4, R6 may be the same or may be different to each other and form an aromatic ring which may have a substituent by combination with the adjacent two carbon atoms.
 less than C-6 greater than 
The optical recording medium according to  less than C-4 greater than , wherein M1 expresses aluminum.
 less than C-7 greater than 
The optical recording medium according to  less than C-1 greater than , wherein a refractive index (n) of a single layer of the recording layer is 1.5xe2x89xa6nxe2x89xa63.0 and an extinction coefficient (k) is 0.02xe2x89xa6kxe2x89xa60.3 against the light having a wavelength range of a recording or reproducing wavelength xc2x15 nm.
 less than C-8 greater than 
The optical recording medium according to  less than C-1 greater than , further comprising a reflective layer containing gold, silver, copper, aluminum, or an alloy thereof.
 less than C-9 greater than 
The optical recording medium according to  less than C-1 greater than , wherein a track pitch on the substrate falls within a range of 0.7 to 0.8 xcexcm, and groove width at a half bandwidth falls within a range of 0.18 to 0.40 xcexcm.
 less than C-10 greater than 
The optical recording medium according to  less than C-1 greater than , wherein the optical recording medium is recordable at a wavelength of 600 to 720 nm.
In the embodiments of  less than C-1 greater than  to  less than C-6 greater than  and  less than C-10 greater than , optical information recording medium capable of recording and reading by a laser light within a wavelength range of 600 nm to 720 nm, and having excellent light resistance and shelf life can be provided. In particular, the optical recording media obtained above are superior in light resistance to those using a squarylium metal chelate compound alone.
In the embodiments  less than C-7 greater than  and  less than C-8 greater than , optical recording media, in addition to having the above-described advantage, capable of recording and reading information at a stably high reflectivity and high degree of modulation can be provided.
In the embodiment  less than C-9 greater than , an optical recording medium, in addition to having the above-described advantages, capable of stably recording and reading information can be provided.
The fourth optical recording medium of the present invention is described below in  less than D-1 greater than . The preferred embodiments of the fourth optical recording medium will be described below in  less than D-2 greater than  to  less than D-8 greater than .
An optical recording medium comprising a substrate and at least a recording layer disposed on the substrate, the recording layer comprises: at least one squarylium compound; and at least one formazan metal chelate compound which comprises a metal and at least one of a formazan compound expressed by one of the following formulae (D-I) and (D-II): 
where, Z expresses a residue forming a 5-membered or 6-membered nitrogen-containing heterocyclic ring which may have a substituent by combination with both the carbon atom and the nitrogen atom bonded to Z, and may be condensed with another aromatic ring; A expresses an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkylcarbonyl group which may have a substituent, an arylcarbonyl group which may have a substituent, an alkenyl group which may have a substituent, a heterocyclic residue which may have a substituent, or an alkoxycarbonyl group which may have a substituent; and B expresses an alkyl group which may have a substituent or aryl group which may have a substituent; 
where, Z1 and Z2 each expresses a residue forming a 5-membered or 6-membered nitrogen-containing heterocyclic ring which may have a substituent by combination with both the carbon atom and the nitrogen atom bonded to Z1 and Z2, respectively, and may be condensed with another aromatic ring; A1 and A2 each independently expresses an alkyl group which may have a substituent, an aryl group which may have a substituent, an alkylcarbonyl group which may have a substituent, an arylcarbonyl group which may have a substituent, an alkenyl group which may have a substituent, a heterocyclic residue which may have a substituent, or an alkoxycarbonyl group which may have a substituent; B1 and B2 each independently expresses an alkylene group which may have a substituent or an arylene group which may have a substituent; W expresses xe2x80x94CH2xe2x80x94 or xe2x80x94SO2xe2x80x94; and m stands for an integer of 0 or 1.
 less than D-2 greater than 
The optical recording medium according to  less than D-1 greater than , wherein the squarylium compound and the formazan metal chelate compound are contained in the recording layer at a weight ratio of 90:10 to 50:50.
 less than D-2 greater than 
The optical recording medium according to  less than D-1 greater than , wherein the metal atom of the formazan metal chelate compound is at least one selected from the group consisting of vanadium, manganese, iron, cobalt, nickel, copper, zinc and palladium, and oxides or halides thereof.
 less than D-3 greater than 
The optical recording medium according to  less than D-1 greater than , wherein the metal atom of the formazan metal chelate compound is at least one selected from the group consisting of vanadium, manganese, iron, cobalt, nickel, copper, zinc and palladium, and oxides or halides thereof.
 less than D-4 greater than 
The optical recording medium according to  less than D-1 greater than , wherein the squarylium compound is at least one of a compound expressed by one of the following formulae (D-III) and (D-VI): 
where, R1 and R2 may be the same or may be different, and each expresses a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic residue which may have a substituent, or R1 and R2 form a heterocyclic ring which may have a substituent by combination with the adjacent nitrogen atom; and R3 is a compound expressed by one of the following formulae (D-IV) and (D-V): 
where, R4 and R5 may be the same or may be different and each independently expresses a hydrogen atom or an alkyl group which may have a substituent, or R4 and R5 form a heterocyclic ring which may have a substituent by combination with the adjacent nitrogen atom; and R6, R7, R8 and R9 may be the same or may be different and each independently expresses a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, a hydroxyl group or a halogen atom, a pair of R4 and R6 or a pair of R5 and R7 may form a nitrogen-containing heterocyclic ring by combination with the adjacent Nxe2x80x94Cxe2x80x94C, the nitrogen-containing heterocyclic ring which may have a substituent: 
where, Q1 expresses a carbon atom or a nitrogen atom, R10 and R11 may be the same or may be different and each independently expresses a hydrogen atom an alkyl group which may have a substituent, an aryl group which may have a substituent, an aralkyl group which may have a substituent or a hydroxyl group, with the proviso that when Q1 expresses a nitrogen atom, R11 does not exist, R12 expresses a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent or an aralkyl group which may have a substituent; R13 and R14 may be the same or may be different and each independently expresses a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent or a halogen atom, or R13 and R14 may form an alicyclic hydrocarbon ring, or an aromatic ring which may have a substituent, or a heterocyclic ring which may have a substituent, by combination with the adjacent two carbon atoms; 
where, Q2 expresses a carbon atom or a nitrogen atom, R15 expresses a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent or a heterocyclic group which may have a substituent, R16 expresses a hydrogen atom, a halogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent, an amino group which may have a substituent or a heterocyclic group which may have a substituent, R17 and R18 may be the same or may be different and each independently expresses an alkyl group which may have a substituent, or R17 and R18 may form an alicyclic hydrocarbon ring or a heterocyclic ring which may have a substituent by combination with the adjacent carbon atom, with the proviso that Q2 expresses a nitrogen atom, R18 does not exist, R19 expresses a hydrogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, or an aryl group which may have a substituent, R20 expresses a halogen atom, an alkyl group which may have a substituent, an aralkyl group which may have a substituent, an aryl group which may have a substituent, a trifluoromethyl group, a nitro group, a cyano group, or an alkoxy group which may have a substituent, n stands for an integer of 0 to 4 with the proviso that when n stands for an integer of 2 to 4, R20s may be the same or may be different from each other and any adjacent two R20s may form an aromatic ring which may have a substituent by combination with the adjacent two carbon atoms.
 less than D-5 greater than 
The optical recording medium according to  less than D-1 greater than , wherein a refractive index (n) of a single layer of the recording layer is 1.5xe2x89xa6nxe2x89xa63.0 and an extinction coefficient (k) is 0.02xe2x89xa6kxe2x89xa60.3 against the light having a wavelength range of a recording or reproducing wavelength xc2x15 nm.
 less than D-6 greater than 
The optical recording medium according to  less than D-1 greater than , further comprising a reflective layer containing gold, silver, copper, or aluminum, or an alloy thereof.
 less than D-7 greater than 
The optical recording medium according to  less than D-1 greater than , wherein a track pitch on the substrate falls within a range of 0.7 to 0.8 xcexcm, and a groove width at a half bandwidth falls within a range of 0.18 to 0.40 xcexcm.
In the embodiments of  less than D-1 greater than  to  less than D-4 greater than  and  less than D-8 greater than , optical information recording media capable of recording and reading by a laser light within a wavelength range of 600 nm to 720 nm, and having excellent light resistance and shelf life can be provided. In particular, the optical recording media obtained above are superior in light resistance to those using a squarylium metal chelate compound alone.
In the embodiments  less than D-5 greater than  and  less than D-6 greater than , optical recording media, in addition to having the above-described advantages, capable of recording and reading information at a stably high reflectivity and high degree of modulation can be provided.
In the embodiment  less than D-7 greater than , an optical recording medium, in addition to having the above-described advantages, capable of stably recording and reading information can be provided.
The optical recording method of the present invention comprises exposing the optical recording medium of the present invention to light beams of 600 to 720 nm, thereby recording information. Accordingly, a novel optical recording method permitting exhibition of the advantages of the above-described optical recording media can be provided.
The optical recording device of the present invention comprises the optical recording medium of the present invention mounted on the substrate. Accordingly, a novel optical recording device permitting exhibition of the advantages of the above-described optical recording medium can be provided.